1. Field of the Invention
The invention relates to a spark plug for an internal combustion engine.
2. Description of the Related Art
Spark plugs serve for electrically igniting a fuel mixture to be combusted in an internal combustion engine. Between a so-called center-electrode and a so-called earth electrode of a spark plug an ignition gap is formed, in which for igniting the fuel mixture an electric ignition spark can form.
Spark plugs are basically distinguished between spark plugs having a hook-shaped earth electrode and spark plugs having an annular earth electrode. Accordingly, DE 10 2011 0277 279 A1 shows a spark plug whose earth electrode is formed hook-like, wherein the ignition gap seen in the axial direction of the center electrode extends axially between an end of the center electrode and an end of the hook-like earth electrode.
A spark plug having an annular earth electrode is known from DE 10 2012 208 069 A1, wherein the ignition gap extends between the center electrode and the earth electrode roundabout the center electrode.
From practice it is known that an earth electrode is composed of two bodies, namely of a first body which is produced from a basic electrode material and of a second body, which is produced from a precious metal, wherein the two bodies are connected to one another, in particular welded together.
With spark plugs known from practice there is the risk that the two bodies of the center electrode become detached from one another and the second body produced from precious metal enters the combustion chamber of the cylinder comprising the spark plug and under certain condition is discharged out of the combustion chamber into the exhaust system of the internal combustion engine. This can cause damage to the internal combustion engine.
There is therefore a need for a spark plug with which the risk that the bodies of the center electrode become detached is reduced.